Referring to FIGS. 9 and 10, a conventional stool 101 is disclosed for a chair 102 for use in an office. The chair 102 includes a base 122 put on the ground, a post 121 installed on the base 122 and a seat 123 installed on the post 121. The stool 101 defines an aperture 111 for receiving the post 121 so that the stool 101 can be put around the post 121 and on the base 122. The base 122 includes five legs each including an inclined upper face. The stool 101 includes a horizontal lower face. To put the stool 101 on the base 122 well, a block 113 is formed on the lower face of the stool 101 and put on the upper face of one of the legs of the base 122. The stool 101 includes a plurality of bosses 112 for massaging the feet of a user sitting in the chair 102. Several problems are, however, encountered in using the stool 101. Firstly, the stool 101 cannot suit users of different sizes for it can be put in only one vertical position and only a horizontal position relative to the post 121. Secondly, it might be difficult for the user to put his or her feet on the stool 101, because it tends to rotate on the post 121. Thirdly, the user feels uncomfortable putting his or her feet on the stool 101 bending his or her legs.
The present invention is therefore intended to obviate or at least alleviate the problems encountered in the prior art.